In many prior art processes for preparing diketones, the diketones are minor by-products or the diketones are prepared by commercially impractical circuitous routes. Some diketones are reported to be prepared by well-known Friedel-Crafts reactions using diacid chlorides and such catalysts as AlCl.sub.3. An example is contained in U.S. Pat. No. 4,816,556 which describes preparation of two diketones by reaction of 2 moles of diphenyl ether with 2 moles terephthalyl chloride (or 2 moles isophthalyl chloride) with 4 moles aluminum chloride as catalyst. Some disadvantages of this process are high cost which results from (1) the use of expensive diacid chlorides instead of diacids and (2) the use of large amounts of catalyst which is destroyed in the workup. Disposal of large amounts of aluminum wastes and corrosion from HCl by-product could also present problems. Another prior art process discloses preparation of a diketone from isophthalic acid and anisole. This process is disclosed by Mitsuru Ueda and Masaki Sato, Makromol. 20, pp. 2675-2678 (1987). This diketone is not the type of this invention since it cannot be polymerized to give a polyketone. The reaction medium was PPMA, which is a mixture of phosphorus pentoxide and methanesulfonic acid, at a particular weight ratio. The phosphorus pentoxide acts as a dehydrator in that it takes up the water that is a product of the reaction and is itself converted to phosphorus acids. This publication also reports the preparation of polyketones by reaction of aromatic diacids containing ether linkages with aromatic compounds containing ether linkages. The authors state that "typical dicarboxylic acids, such as isophthalic acid and terephthalic acid, cannot be used."
Another prior art publication which may be relevant to the present invention is Mitsuru Ueda and Toshiya Kano, Makrol. Chem., Rapid Commun., 5, pp. 833-836 (1985). This paper reports preparation of the following diketone in PPMA under specific reaction conditions: ##STR1## wherein PH is phenyl. This publication also reports the preparation of polymers from aliphatic diacids and difunctional aromatic compounds. Isophthalic acid did not give polymers, only low oligomer. No work with terephthalic acid was reported.
Another publication which may be relevant to the present invention is U.S. Pat. No. 4,453,010. This patent discloses the preparation of aromatic hydroxyketones in methanesulfonic acid without a dehydrator such as phosphorus pentoxide. An aromatic acid reacts with a hydroxy-containing aromatic compound to give a hydroxyketone.
None of the above publications disclose preparation of a keto-acid.
It would be highly desirable to have a process for preparing diketones and keto-acids that overcomes the problems of prior art processes.